This application relates generally to gas turbine engines and, more particularly, to a method and apparatus for performing gas turbine engine maintenance.
Gas turbine engines generally include, in serial flow arrangement, a high-pressure compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high temperature gas stream, and a high pressure turbine. The high-pressure compressor, combustor and high-pressure turbine are sometimes collectively referred to as the core engine. Such gas turbine engines also may include a low-pressure compressor, or booster, for supplying compressed air to the high pressure compressor.
At least some known gas turbine engines also include at least one variable stator vane (VSV) assembly that is utilized to control the quantity of air flowing through the high-pressure compressor to facilitate optimizing the performance of the high-pressure compressor. The variable stator vane assembly includes a plurality of variable stator vanes which extend between adjacent rotor blades. The variable stator vanes are rotatable about an axis such that the stator vanes are positionable in a plurality of orientations to direct air flow through the high-pressure compressor. Moreover, at least some known gas turbine engines include a variable bypass valve (VBV) that is configured to bypass a portion of the pressurized air generated by a booster stage, i.e. the low pressure compressor, around the high-pressure compressor to facilitate matching the output of the booster stage to the input requirements of the high-pressure compressor.
To facilitate operating the VSV's and the VBV, at least one known gas turbine engine includes a fuel system that is configured to channel fuel to an actuator that is actuated utilizing an engine control system. More specifically, as the gas turbine engine is operated, the engine control system electrically actuates the actuator such that fuel supplied by the fuel pump, is channeled to either the VSV's and/or the VBV to facilitate repositioning either the VSV's and/or the VBV.
When the gas turbine engine receives a shutdown command, the engine control system, based on at least one predetermined engine operating parameter, ceases to provide the actuator any operational commands such that the VSV's and the VBV will “drift” to a failsafe operating position.
Accordingly, to service the gas turbine engine, maintenance personnel must reposition the VSV's and/or the VBV to a desired position. For example, to borescope the gas turbine engine, the maintenance personnel will reposition the VSV's to a fully open position, and reposition the VBV to a fully closed position. To reposition either the VSV's and/or the VBV, the maintenance personnel disconnect the fuel line between the fuel pump and the engine control system, and install a hand pump to facilitate channeling fuel to either the VSV's and/or the VBV. More specifically, the handpump is operated to either open and/or close at least one the VSV's and the VBV when the gas turbine engine is not operating.
However, utilizing a handpump to reposition either the VSV's and/or the VBV increases the time and thus the cost of maintaining the gas turbine engine. Moreover, when the fuel line between the fuel pump and the engine control system is reconnected, the gas turbine engine must be operated in a test configuration to verify that the fuel system is not leaking. Accordingly, utilizing a hand pump to reposition either the VSV's and/or the VBV increases the time and thus the cost to perform maintenance on the gas turbine engine.